This invention relates to opacified latex paints. Conventional latex paints are prepared by dispersing sufficient opacifying pigment such as titanium dioxide into film-forming transparent polymeric binders to provide an opacified paint film. Opaque or decorative paint films have been suggested based on the presence of air voids in the paint films such as provided by cellular or vesiculated particles in British Pat. No. 1,178,162, Canadian Pat. No. 856,863, and British Pat. No. 1,192,492. Opacification has been further achieved by entrapping air in the film to provide voids in the paint film and generally are referred to as bubble coatings. Such coatings have only limited opacity and primarily function as decorative or semi-opaque coatings rather than conventional opacified paint coatings. Hence, the best opacified paint films are conventional latex paints compounded with titanium dioxide and extender pigments such as calcium carbonate.
A conventional parameter for describing prior art latex paints is the pigment-volume-content (PVC) which is the percent by volume of pigment present in the dried paint film relative to the total volume of the dried paint film. At a certain PVC, the volume of pigments in the paint film abruptly causes considerable air voids in the dry paint film due to binder deficiency. The PVC measurement at this level of pigment content is characterized as critical-PVC wherein a binder deficiency occurs such that insufficient binder is present in the paint film to encapsulate the pigment particles and fill any remaining voids in the film. At the onset of such porosity in the paint film due to binder deficiency, the physical durability properties of the dried paint film abruptly diminish with higher PVC's thereby causing a substantial drop or discontinuity of physical properties of conventional paint films due to increased pigment loading. In conventional prior art latex paints, opacity and porosity exhibit approximately the same sensitivity to the onset of air voids in the paint film wherein opacity increases with increased film porosity but most paint film physical properties (except opacity) such as scrub resistance and enamel holdout abruptly diminish at approximately the same PVC which has been known in prior art paints as a critical-PVC. Conventional prior art paints suffer a drastic loss of enamel holdout properties simultaneous with achieving increased opacity or hiding characteristics of the paint film with the result that the critical-PVC of conventional latex paints is a narrow PVC range (FIG. 1) wherein the critical-PVC is generally a compromise at a point of minimum opacity (for given TiO.sub.2 level) and maximum paint film physical properties.
It now has been found that latex paints containing solid non-film-forming plastic pigment and opacifying pigments provide hard, dried paint films having substantially increased opacity as well as substantially improved physical properties. Improved opacity is obtained over a wide range of PVC's before the onset of excessive porosity in the paint film whereby the preferred useful range of PVC's of the paint of this invention incorporates both maximum opacity and maximum enamel holdout as well as other optimized physical properties. This invention broadly provides for improved latex paints having a PVC above the critical-PVC and capable of providing good opacified paint films having desirable paint film integrity properties.
Accordingly, a primary object of this invention is to provide an improved latex dispersion paint having a wide range of PVC's above the critical-PVC as measured by opacity for providing substantially improved paint films having high PVC's while retaining good paint film characteristics.
These and other advantages of this invention will become more apparent by referring to the drawings and the Detailed Description of the Invention.